Electric and hybrid vehicle propulsion systems typically employ an alternating current (AC) motor drive inverter to transform direct current (DC) voltage of the energy storage battery to variable speed AC waveforms in order to drive the electric motor. Most commonly, the inverter uses a current controlled voltage source configuration. Power semiconductor switches, such as, for example, insulated gate bipolar transistors (or IGBTs) can be used to pulse width modulate (PWM) the voltage applied to the motor. The motor acts as a large filter and smooths the waveforms such that the current becomes nearly sinusoidal.
In high performance vehicles, it may be desired to have a large motor torque. Torque is roughly proportional to the current, so a high performance vehicle typically requires a large AC current to drive the motor, making protection circuits even more essential.